The present invention relates to free-electron lasers, particularly to the use of an inverse free-electron laser (IFEL) as a viable vacuum laser acceleration process, and more particularly to using an ultrahigh intensity chirped laser pulse whereby the dephasing length can be increased considerably, thus yielding high gradient IFEL acceleration, and which results in a compact, efficient vacuum laser accelerator.
The inverse free-electron laser interaction has been proposed as a viable vacuum laser acceleration process. See R. B. Palmer, J. Appl. Phys. 43, 3014 (1972); and E. D. Courant, et al., Phys. Rev. A32, 2813 (1985). Pioneering experimental work performed at Columbia University first demonstrated IFEL acceleration, see I. Wernick, et al., Phys. Rev. A46, 3566 (1992), and this was followed by experiments using a ns-duration gigawatt, CO2 laser at Brookshaven National Laboratory, see A. Van Steenbergan, et al., Phys. Rev. Lett. 77, 2690 (1996). One of the fundamental limitations of the acceleration scheme is the dephasing of the trapped electron with respect to the drive laser wave: as the electron energy increases, the free-electron laser (FEL) resonance condition cannot be maintained, and the electron reaches a maximum energy given by the FEL interaction bandwidth. See T. C. Marshall, Free-Electron Lasers (McMillan Publishing Co., New York, N.Y. 1985) and C. W. Roberson and P. Sprangle, Phys. Fluids B1, 3 (1989).
The present invention involves the IFEL interaction in a different regime, using ultrashort, TW-class drive laser pulses which are now routinely generated by tabletop systems using chirped pulse amplification (see M. D. Perry, et al., Science 264,917 (1994). By the use of a chirped laser pulse, such allows the FEL resonance condition to be maintained beyond the conventional dephasing limit, thus further improving the electron energy gain. The ultrashort, high intensity chirped laser pulses thus generated provide an IFEL with high accelerating gradients ( greater than GeV/m), in contrast with the longer pulse approaches previously considered. Thus, the dephasing problem of the prior IFEL approach is alleviated by using a chirped drive laser pulse.
It is an object of the present invention to alleviate the dephasing problem on inverse free-electron lasers.
A further object of the invention is to provide an inverse free-electron laser (IFEL) with a chirped drive laser pulse.
A further object of the invention is to provide a compact, efficient vacuum laser accelerator.
Another object of the invention is to provide a chirped pulse inverse free-electron laser vacuum accelerator.
Another object of the invention is to provide an IFEL with an ultrahigh intensity chirped laser pulse, whereby the dephasing length is increased, thus yielding high gradient IFEL acceleration.
Other objects and advantages of the present invention will become apparent from the following description and accompanying drawings. The present invention builds upon the inverse free-electron laser acceleration process. High gradient acceleration is normally precluded by the dephasing of the accelerated electron with respect to the drive laser pulse. In this invention the dephasing problem is alleviated by using a chirped drive laser pulse. In this manner, the frequency of the drive laser pulse remains resonant with the electron as it accelerates through the wiggler. This technique is similar to the use of a tapered wiggler but it is an all-optical arrangement which is more flexible and easier to implement. In addition this invention allows for more control over the acceleration and permits staging of the interaction to achieve high energies. Thus, this invention results in a compact, efficient IFEL vacuum laser accelerator.